Abstract

Background

The powdery mildew disease represents a valuable patho-system to study the interaction
between plant hosts and obligate biotrophic fungal pathogens. Numerous discoveries
have been made on the basis of the quantitative evaluation of plant-powdery mildew
interactions, especially in the context of hyper-susceptible and/or resistant plant
mutants. However, the presently available methods to score the pathogenic success
of powdery mildew fungi are laborious and thus not well suited for medium- to high-throughput
analysis.

Results

Here we present two new protocols that allow the rapid quantitative assessment of
powdery mildew disease development. One procedure depends on quantitative polymerase
chain reaction (qPCR)-based evaluation of fungal biomass, while the other relies on
the quantification of fungal conidiospores. We validated both techniques using the
powdery mildew pathogen Golovinomyces orontii on a set of hyper-susceptible and resistant Arabidopsis thaliana mutants and found that both cover a wide dynamic range of one to two (qPCR) and four
to five (quantification of conidia) orders of magnitude, respectively. The two approaches
yield reproducible results and are easy to perform without specialized equipment.

Conclusions

The qPCR and spore count assays rapidly and reproducibly quantify powdery mildew pathogenesis.
Our methods are performed at later stages of infection and discern mutant phenotypes
accurately. The assays therefore complement currently used procedures of powdery mildew
quantification and can overcome some of their limitations. In addition, they can easily
be adapted to other plant-powdery mildew patho-systems.